Hydrogen cyanide is highly toxic, but a commercially important chemical compound having a wide variety of industrial uses. Hydrogen cyanide is produced commercially by contacting ammonia excess hydrocarbon gas, and an oxidizing gas with a platinum-group-metal catalyst. The excess hydrocarbon gas is ignited, and the heat generated is sufficient to cause the endothermic reaction of ammonia and the remaining hydrocarbon gas to form hydrogen cyanide.
Shipment of hydrogen cyanide presents potential hazards. One way to avoid these potential hazards is to produce the product at the site where it is to be used. However this requires the installation of a large number of small production facilities. Such production facilities have in the past been expensive.
It is an objective of the present invention to provide a process for the production of HCN that can be operated on a relatively small scale but efficiently and at low a installation cost.
The present invention employs the use of single mode microwave heating of a platinum-group-metal catalyst to cause ammonia to react with hydrocarbon gas and form hydrogen cyanide. The reaction is endothermic, and by the use of microwave heating the amount of energy used may be carefully regulated so that a minimum of energy is wasted.
A single mode microwave cavity is a metallic chamber, where at least two of the three dimensions are approximately half the microwave operating wavelength. The cavity then produces a "standing wave", where intense electric fields are produced. These fields are usually in the center of the cavity.
The use of microwave energy without interaction with a solid catalyst to produce HCN from ammonia and methane at pressures of 10 to 25 torr is disclosed in a thesis titled "Chemical Physics in a Microwave Plasma--Production of HCN." by Thorkild Juul-Dam, University of Texas at Austin, June 1942.
SUMMARY OF THE INVENTION
The present invention is a process for the preparation of hydrogen cyanide which comprises passing a mixture of ammonia vapor and a hydrocarbon gas having 1 to 6 carbon atoms at a pressure at least equal to atmospheric pressure in contact with a platinum-group-metal catalyst containing 0.1 to 20% by weight platinum-group metal, while subjecting the catalyst to single mode microwave heating to raise the temperature of the catalyst to reaction temperature, and recovering hydrogen cyanide.
The present invention is also a product generator comprising:
a microwave power source;
a waveguide coupled to said power source for transmitting microwave radiation therethrough; said waveguide having a flared section;
a resonant cavity attached to the flared section of said waveguide, said resonant cavity having a movable wall opposite the side of the cavity to which the waveguide is attached for tuning the resonant cavity and for focusing microwave radiation on a tubular reactor;
a tubular reactor extending through said resonant cavity intermediate between the side of the cavity to which the waveguide is attached and the movable wall, in a direction parallel to the movable wall, said tubular reactor having inlet means for introducing gas and outlet means for removing product, the portion of the tubular reactor inside the resonant cavity being adapted to contain a catalyst.